Some rotary drilling rigs use a square or hexagonal pipe, often called the Kelly, which is rotated by a rotary table, to rotate the drill string. A rotary bit located at the bottom of the drill string is commonly use to cut an earth-bore, often referred to as the hole. Drilling fluid, often called drilling mud or simply mud is circulated thru the drill pipe and up the annulus of the hole to, among other reasons, remove the drill cuttings from the hole. Installed between the bottom of the Kelly and the drill pipe may be a mud saver which has a valve which uses a coil spring to close when the drill string is unscrewed, sometimes referred to as broken, from the Kelly. The purpose of the mud saver valve sub is to stop the flow of mud through the Kelly when it is disconnected from the drill string.
Some rotary drilling rigs utilize what is commonly referred to as a top drive to rotate the drill sting. A top drive moves the drill string up and down and rotates it without need of Kelly and rotary table to turn the Kelly. Unfortunately, a top drive has a limitation, namely there is not enough room for a typical mud saver valve sub between the top drive and the drill pipe. The typical mud saver valve used in Kelly drive rotary drilling is too long for use with a top drive. Because of this limitation top drive systems often use a lower inside blow out presented, sometimes called an IBO, to reduce spillage of drilling mud. The top drive will typically have a rotating dog that trips the IBO to close when the drill string is disconnected from the drive assembly. However, the primary purpose of the IBO is to prevent uncontrolled well blow outs thru the inside of the drill pipe. It is risky to use the IBO for mud saving/checking, in that, at some point in it's use, the IBO wears to the point that may not be able to control a blow out, thereby presenting risk to property and personnel.
The time that it takes to close the top drive valve to save or hold the mud in the top drive system and then to later reopen the top drive valve IBO is valuable. A deepwater drilling rig may cost well over 500,000 dollars per day to operate. Drilling at 60 feet per hour, use of the invention disclosed could be expected to reduce time for each connection by at least 2 minutes, resulting in time-for-connection reduction of least an hour per day. This equates into approximately 20,000 dollars a day or more in rig-time savings, in addition to reducing mud costs, increased safety and environmental benefits. Because of the risk it takes to use an IBO to reduce mud spillage some drillers prefer to use a hydraulic mud bucket to catch the mud and transfer the mud to the mud pit system on the rig. This is even more time consuming, and results in utilizing even more, expensive, rig-time that using the IBO to reduce mud spillage.